A newly upgraded version of the BCVEGPY, a generator for hadronic production of the meson $B_c$ and its excited states, is available. In comparison with the previous one [C.H. Chang, J.X. Wang and X.G. Wu, Comput. Phys. Commun. {bf 175}, 624 (2006)],
the new version is to apply an improved hit-and-miss technology to generating the un-weighted events much more efficiently under various simulation environments. The codes for production of $2S$-wave $B_c$ states are also given here.
A valid prediction for a physical observable from quantum field theory should be independent of the choice of renormalization scheme -- this is the primary requirement of renormalization group invariance (RGI). Satisfying scheme invariance is a chall
enging problem for perturbative QCD (pQCD), since a truncated perturbation series does not automatically satisfy the requirements of the renormalization group. Two distinct approaches for satisfying the RGI principle have been suggested in the literature. One is the Principle of Maximum Conformality (PMC) in which the terms associated with the $beta$-function are absorbed into the scale of the running coupling at each perturbative order; its predictions are scheme and scale independent at every finite order. The other approach is the Principle of Minimum Sensitivity (PMS), which is based on local RGI; the PMS approach determines the optimal renormalization scale by requiring the slope of the approximant of an observable to vanish. In this paper, we present a detailed comparison of the PMC and PMS procedures by analyzing two physical observables $R_{e+e-}$ and $Gamma(Hto bbar{b})$ up to four-loop order in pQCD. At the four-loop level, the PMC and PMS predictions for both observables agree within small errors with those of conventional scale setting assuming a physically-motivated scale, and each prediction shows small scale dependences. However, the convergence of the pQCD series at high orders, behaves quite differently: The PMC displays the best pQCD convergence since it eliminates divergent renormalon terms; in contrast, the convergence of the PMS prediction is questionable, often even worse than the conventional prediction based on an arbitrary guess for the renormalization scale. ......
The $B_c$ meson is a doubly heavy quark-antiquark bound state and carries flavors explicitly, which provides a fruitful laboratory for testing potential models and understanding the weak decay mechanisms for heavy flavors. In view of the prospects in
$B_c$ physics at the hadronic colliders as Tevatron and LHC, $B_c$ physics is attracting more and more attention. It has been shown that a high luminosity $e^+e^-$ collider running around the $Z^0$-peak is also helpful for studying the properties of $B_c$ meson and has its own advantages. For the purpose, we write down an event generator for simulating $B_c$ meson production through $e^+e^-$ annihilation according to relevant publications. We name it as BEEC, in which the color-singlet $S$-wave and $P$-wave $(cbar{b})$-quarkonium states together with the color-octet $S$-wave $(cbar{b})$-quarkonium states can be generated. BEEC can also be adopted to generate the similar charmonium and bottomnium states via the semi-exclusive channels $e^{+}+e^{-}rightarrow |(Qbar{Q})[n]rangle +Q +bar{Q}$ with $Q=b$ and $c$ respectively. To increase the simulation efficiency, we simplify the amplitude as compact as possible by using the improved trace technology. BEEC is a Fortran programme written in a PYTHIA-compatible format and is written in a modularization structure, one may apply it to various situations or experimental environments conveniently by using the GNU C compiler {bf make}. A method to improve the efficiency of generating unweighted events within PYTHIA environment has been suggested. Moreover, BEEC will generate a standard Les Houches Event data file that contains useful information of the meson and its accompanying partons, which can be conveniently imported into PYTHIA to do further hadronization and decay simulation.
We present an improved version of GENXICC, which is a generator for hadronic production of the doubly heavy baryons $Xi_{cc}$, $Xi_{bc}$ and $Xi_{bb}$ and has been raised by C.H. Chang, J.X. Wang and X.G. Wu [Comput. Phys. Commun. 177 (2007) 467; Com
put. Phys. Commun. 181 (2010) 1144]. In comparison with the previous GENXI
In the present paper, we provide an addendum to improve the efficiency of generating unweighted events within PYTHIA environment for the generator BCVEGPY2.1 [C.H. Chang, J.X. Wang and X.G. Wu, Comput.Phys.Commun.{bf 174}, 241(2006)]. This trick is h
elpful for experimental simulation. Moreover, the BCVEGPY output has also been improved, i.e. one Les Houches Event common block has been added so as to generate a standard Les Houches Event file that contains the information of the generated $B_c$ meson and the accompanying partons, which can be more conveniently used for further simulation.
We present an improved calculation on the pionic twist-3 distribution amplitudes $phi^{pi}_{p}$ and $phi^{pi}_{sigma}$, which are studied within the QCD sum rules. By adding all the uncertainties in quadrature, it is found that $<xi^2_p>=0.248^{+0.07
6}_{-0.052}$, $<xi^4_p>=0.262^{+0.080}_{-0.055}$, $<xi^2_sigma>=0.102^{+0.035}_{-0.025}$ and $<xi^4_sigma>=0.094^{+0.028}_{-0.020}$. Furthermore, with the help of these moments, we construct a model for the twist-3 wave functions $psi^{pi}_{p,sigma}(x,mathbf{k}_bot)$, which have better end-point behavior and are helpful for perturbative QCD approach. The obtained twist-3 distribution amplitudes are adopted to calculate the $Btopi$ transition form factor $f^+_{Bpi}$ within the QCD light-cone sum rules up to next-to-leading order. By suitable choice of the parameters, we obtain a consistent $f^+_{Bpi}$ with those obtained in the literature.
